#define versus a constant variable

[blangela]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

Thanks,

Bob

 

[Victor Bazarov]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

I guess you could search for "Macros are evil", both in the FAQ and
in the archives.

V

 

[Salt_Peter]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

Thanks,

Bob

pros: none
cons: #define is not type safe

And more importantly, a constant variable is an object, a #define is
not

 

[faceman28208]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

There are no pros to using #define.

The most likely "con" is that symbols defined by the preprocessor are
not available in the debugger (except for one compiler I have worked
with).

The next most likely "con" is unexpected text substitutions.

Another con is your value might get redefined.

 

[Marcus Kwok]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

Well, a short list is given in the FAQ:
http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.7

 

[Ron Natalie]

pros: none
cons: #define is not type safe

The con above is bullshit. The type is just as safe as anything
else (at least if we are talking numerics and string literals which
is usually what is involved).

The biggest problem is that they don't have scoping.

 

[Juha Nieminen]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

A #define has always global scope in the current compilation unit
(ie. the source file where it's defined) regardless of where you
define it, while a const variable can have any scope (all the way
from global to the whole program to local to one {} block).

You can't have a pointer to a #defined constant, but you can to a
const variable.

A #define can basically only define internal types (ints, etc),
while a const variable can define anything, such as std::strings
and so on.

 

[Ron Natalie]

A #define has always global scope in the current compilation unit
(ie. the source file where it's defined) regardless of where you
define it, while a const variable can have any scope (all the way
from global to the whole program to local to one {} block).

Actually it totally disregards scope. It doesn't even obey the syntax
rules that an identifier would.

 

[ajk]

Can somepoint me to a good discussion on the pros and cons of using
#define versus a constant variable in your C+ application?

Thanks,

Bob

constants are more flexible than #define's

#define C "1"

const char *C = "1";

char const *C = "1";

so u can decide what the user can do with it.


--

#define C myclass(123)

const myclass C = myclass(123);

in the former case typically several instances are created of
myclass(123) however in the latter, only one is created.

br/ajk

 

[BobR]

constants are more flexible than #define's
#define C "1"

const char *C = "1";
char const *C = "1";

Those two are identical. Did you mean:
char const *C = "1"; // same as 'const char'. 'char' is ro.
char * const C = "1"; // pointer is ro. 'char' is rw.

[ ro == read-only, rw == read-write ]